The technical portion of the work carried out by an optician consists in mounting a pair of ophthalmic lenses in or on the frame selected by the user, in such a manner that each lens is suitably positioned facing the corresponding eye of the user so as to perform as well as possible the optical function for which it is designed. In order to do this, it is necessary to perform a certain number of operations.
After the frame has been selected, the optician must begin by situating the position of the pupil of each eye in the frame of reference of the frame. The optician thus determines mainly two parameters that are associated with the morphology of the user, namely the pupillary distance and the height of the pupil relative to the frame.
For the frame itself, it is necessary to identify its shape, and this is generally done by means of a pattern or an apparatus specially designed to read the inner contour of the rim (i.e. the part of the frame that goes round the lens), or else from an electronic file that is prerecorded or supplied by the manufacturer.
From the above geometrical input data, it is necessary to cut each lens to shape. A lens is cut to shape for mounting in or on the frame selected by the future user by modifying the outline of the lens so as to match it to that of the frame and/or to the shape desired for the lens. Cutting to shape comprises an edging operation for shaping the periphery of the lens, and depending on whether the frame is of the rimmed type or of the rimless type with local clamping through fastener holes formed in the lens, appropriately beveling and/or drilling the lens. Edging (or cutting out proper) consists in eliminating the superfluous peripheral portion of the ophthalmic lens in question so as to reduce its outline, which is usually initially circular, to the arbitrary outline of the rim or surround of the eyeglasses frame in question, or merely to the pleasing shape desired when the frame is of the rimless type. This edging operation is usually followed by a chamfering operation which consists in dulling or chamfering the two sharp edges around the edged lens. When the frame is of the rimmed type, the chamfering is accompanied by beveling which consists in forming a rib usually referred to as a bevel, generally of triangular cross-section with a top that is rounded or interrupted by a counter-bevel on the edge face of the ophthalmic lens. The bevel is for engaging in a corresponding groove, also known as a bezel, formed in the rim or the surround of the eyeglasses frame in which the lens is to be mounted. When the frame is of the rimless type, the cutting out of the lens and optionally the dulling of its sharp edges (chamfering) are followed by appropriately drilling the lenses to enable it to be secured to the temples and to the bridge of the rimless frame. Finally, when the mounting is of the type having a rim of Nylon string, the chamfering is accompanied by grooving consisting in forming a groove in the edge face of the lens, the groove being for receiving the mounting Nylon string for pressing the lens against the rigid portion of the frame.
Usually, these edging, chamfering, and beveling operations are performed in succession on a single machine tool, known as an “edger” and provided with a set of suitable cutter/grinder bits. Drilling can be performed on the edger which is then fitted with corresponding drill bits, or else on a separate drilling machine.
The optician must also perform a certain number of measurement and/or identification operations on the lens itself prior to cutting out in order to identify certain characteristics such as, for example: the optical center if the lens is a single-vision lens or the mounting cross if the lens is a progressive lens, or the direction of the axis of progression and the position of the centering point if the lens is a progressive lens. In practice, the optician marks certain characteristic points using a marker tip on the ophthalmic lens itself. These marks are used for securing a chuck receiver or centering-and-drive pad on the lens enabling the ophthalmic lens to be positioned correctly in the edger that is to give it the desired outline, corresponding to the shape of the selected frame. The pad is usually stuck temporarily on the lens by means of a double-sided adhesive. This operation is commonly referred to as “centering” the lens, or by extension, “blocking” the lens, insofar as the pad can be used subsequently for blocking purposes, i.e. for preventing the lens from moving relative to the means for cutting it to shape in a geometrical configuration that is known because of the pad.
After the centering pad has been put into place, the lens fitted in this way is then placed in the cutting-out machine where it is given the shape that corresponds to the shape of the selected frame. The centering pad serves to define and physically to embody on the lens both a geometrical frame of reference in which characteristic points and directions of the lens are identified, with this being necessary for the lens to be positioned properly relative to the pupil, and also cutting out values for ensuring that these characteristic points and directions are properly positioned in the frame.
In certain circumstances, it can happen that the first attempt at cutting out the lens does not lead to the lens being properly mounted in the frame. The operator must then machine the lens again. To do this, the lens is replaced in the machine and is held stationary on its clamping shaft using the same pad, thus making it possible to reuse the frame of reference that was used for the initial cutting-out operation.
Depending on the organization and the equipment available to the optician, the above-mentioned operations can be spread over two or three distinct workstations. Each lens being processed must therefore be transferred from one workstation to another. Inaccuracies, errors, or accidents can then arise because of the large amount of handling. In addition, if the operations are performed in the context of an industrial organization, that gives to a considerable loss of time and to high production costs. In addition, the risk of damaging the ophthalmic lens increases with the amount of handling, thereby considerably lengthening time to delivery and further increasing costs.
Document FR 2 825 308 and its equivalent EP 1 392 472 propose optimizing the above-specified process by automating some of the measurement and positioning stages applied to the ophthalmic lens, thus making it possible to determine the optical characteristics of the lens and to control the stage of transporting said lens to the cutting-out station and the cutting-out stage proper.
The device proposed therein comprises means for measuring identification characteristics of said lens and means for cutting said lens to shape, enabling the outline of the lens to be brought to the desired shape. Conventionally, the cutting-out means are constituted by an edger which has a set of grindwheels and means for blocking and driving the lens in rotation constituted by two rotary shafts on the same axis mounted to move axially to pinch the lens on its axis like a clamp. To enable the lens to be moved towards or away from the grindwheels while machining is taking place, the clamping and drive shafts are carried by a transversely-movable rocker (movable in pivoting or in translation). Partial automation of the process of preparing the lens is obtained by a sliding reception and transfer carriage arranged to transfer the ophthalmic lens through two transfers between three positions, with transfer from a measurement position in which the ophthalmic lens is presented to the measurement means to an intermediate position distinct from the measurement position, and then transfer from said intermediate position to a cutting-out position distinct from the intermediate and measurement positions.
However, in that device, the lens is transferred from its intermediate position to the cutting-out means directly by the clamping and rotary drive spindles of the cutting-out means, by taking advantage of the ability of the rocker carrying the spindles of the edger to move transversely. That way of transferring the lens to the cutting-out means provides the combined advantages of saving on means and of conserving the frame of reference of the lens as detected by the measurement means. However to achieve that it imposes limitations that are penalizing.
Above all, existing devices are found to be functionally insufficient. While preparing a lens for mounting purposes it is necessary to perform one or more feeling operations on the lens. All of those feeling operations are conventionally performed on the edger, such that the lenses can be processed in sequential manner only, with it being possible to begin cutting out only after feeling has been completed, and with it being impossible to feel any other lens. It will be understood that the feeling operation occupies the cutting-out means and makes them unavailable for their main function of cutting out. However, it is known that the cutting-out step is the longer step and can be performed automatically without requiring particular supervision, thereby releasing the operator. In other words, the cutting-out means, which are expensive and often present as a single unit on the premises of an optician, are occupied for a secondary task that does not in itself justify the complexity and the expense of said means. Above all, this leads to a loss of precious time for the operator or the optician who cannot then pay attention to tasks of greater added value that require that person's competence.
Without complicating the mechanism of the edger members (with the inaccuracy and increasing cost that that would entrain), the lens can be felt on the edger only after the lens has been blocked and with the feeler having restricted degrees of freedom. However, performing a feeling operation prior to blocking could provide geometrical information useful in achieving accurate blocking of the lens, and studies performed by the Applicant show that lack of such prior feeling operations can be penalizing on the accuracy and the reliability of feeling, and thus of blocking, and hence of the cutting-out operation as a whole. This lack of accuracy in blocking is particularly penalizing when reworking a lens that has already been cut out poorly.